In the manufacture of printed circuit boards, copper surfaces are coated with various organic films, including etch resists, plating resists, solder masks and other dielectric materials. These films can be applied to the board surfaces as a liquid or as a dry film resist. In any case, good adhesion of the film to the surfaces is necessary in order to prevent the film from etching off or flaking from the surfaces.
In some cases, such as with solder masks, the film remains permanently on the surfaces after it has been applied thereto. In this instance, a tight bond to the copper surfaces is required since the mask protects certain areas of the copper surfaces prior to contact with molten solder during the soldering process or prior to treatment with corrosive chemicals which come into contact with the uncoated areas before metal layers are deposited.
In other instances, such as when an etch resist is used, the film remains on the copper surfaces only temporarily. Good adhesion is necessary because the etch resist protects certain areas of the copper surfaces against an attack from corrosive chemicals used to remove copper areas being exposed by etching. After the resist has been etched, it is removed again.
Improving adhesion of an organic film on a smooth copper surface typically is accomplished by roughening the surfaces. This may be carried out by mechanical means, for example by grinding or by treatment of the surface with a slurry of pumice in water. In the alternative, the surfaces may be roughened by chemical means (e.g., microetching), with solutions based on persulfates or hydrogen peroxide and sulfuric acid (among others).
In the manufacture of printed-wiring boards, copper surfaces are roughened in order to improve adhesion of etching resists or solder resists to be coated on the copper surfaces. Microetching is also used for improving solderability, for example, as a pretreatment for a solder coating step or for removing oxides from copper surfaces before soldering electronic parts.
These roughening methods have proven problematic in that the organic films do not have sufficient adhesion to the copper surfaces if they are deposited onto the copper surfaces of very narrow conductor lines and onto extremely fine solder pads or bond pads. Improved etching compositions are needed that provide a good grain structure on the copper surface and provide good adhesion during solder mask applications.
It is an object of the present invention to provide a surface treating composition for copper and copper alloys which can exhibit excellent adhesiveness to solder resists and the like and provide roughened surfaces of copper or copper alloys with adequate surface structure and superior solderability.